Re: [Qemu-devel] [PATCH v2] qapi: report the default CPU type for each machine

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 12 Jun 2019 13:41:25 +0200
Daniel P. Berrangé <berrange@redhat.com> wrote:

> When user doesn't request any explicit CPU model with libvirt or QEMU,
> a machine type specific CPU model is picked. Currently there is no way
> to determine what this QEMU built-in default is, so libvirt cannot
> report this back to the user in the XML config.
> 
> This extends the "query-machines" QMP command so that it reports the
> default CPU model typename for each machine.
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Reviewed-by: Igor Mammedov <imammedo@redhat.com>


we probably need to allow feed it back to QEMU -cpu directly
for all machines (currently it will work only with a handfull of them)
something like:

diff --git a/exec.c b/exec.c
index e7622d1956..ea4d2d74a6 100644
--- a/exec.c
+++ b/exec.c
@@ -999,11 +999,14 @@ const char *parse_cpu_option(const char *cpu_option)
         exit(1);
     }
 
-    oc = cpu_class_by_name(CPU_RESOLVING_TYPE, model_pieces[0]);
-    if (oc == NULL) {
-        error_report("unable to find CPU model '%s'", model_pieces[0]);
-        g_strfreev(model_pieces);
-        exit(EXIT_FAILURE);
+    oc = object_class_by_name(model_pieces[0]);
+    if (!oc) {
+        oc = cpu_class_by_name(CPU_RESOLVING_TYPE, model_pieces[0]);
+        if (oc == NULL) {
+            error_report("unable to find CPU model '%s'", model_pieces[0]);
+            g_strfreev(model_pieces);
+            exit(EXIT_FAILURE);
+        }
     }
 
     cpu_type = object_class_get_name(oc);

> ---
> 
> Changed in v2:
> 
>  - Fix qapi docs version tag
> 
>  qapi/misc.json | 6 +++++-
>  vl.c           | 4 ++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/qapi/misc.json b/qapi/misc.json
> index 8b3ca4fdd3..9e2dedd938 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -2018,12 +2018,16 @@
>  #
>  # @hotpluggable-cpus: cpu hotplug via -device is supported (since 2.7.0)
>  #
> +# @default-cpu-type: default CPU model typename if none is requested via
> +#                    the -cpu argument. (since 4.1)
> +#
>  # Since: 1.2.0
>  ##
>  { 'struct': 'MachineInfo',
>    'data': { 'name': 'str', '*alias': 'str',
>              '*is-default': 'bool', 'cpu-max': 'int',
> -            'hotpluggable-cpus': 'bool'} }
> +            'hotpluggable-cpus': 'bool',
> +            '*default-cpu-type': 'str'} }
>  
>  ##
>  # @query-machines:
> diff --git a/vl.c b/vl.c
> index 201144b162..b2de329bd2 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1519,6 +1519,10 @@ MachineInfoList *qmp_query_machines(Error **errp)
>          info->name = g_strdup(mc->name);
>          info->cpu_max = !mc->max_cpus ? 1 : mc->max_cpus;
>          info->hotpluggable_cpus = mc->has_hotpluggable_cpus;
> +        if (mc->default_cpu_type) {
> +            info->default_cpu_type = g_strdup(mc->default_cpu_type);
> +            info->has_default_cpu_type = true;
> +        }
>  
>          entry = g_malloc0(sizeof(*entry));
>          entry->value = info;